This invention relates to a general purpose nut cracking machine that has particular application to the cracking of macadamia nuts, and other nuts that are problematical because of their hard shell or smooth surface. The nut cracking machine of this invention, relates to the nut cracking machines of our earlier issued U.S. Pat. No. 4,793,248 issued, Dec. 27, 1988, entitled, NUT SHELLING MACHINE, and our issued U.S. Pat. No. 5,115,733, issued May 26, 1992, entitled NUT SHELLING MACHINE, Both these previously developed machines were directed at the problem of efficiently shelling the macadamia nut with the objective of minimizing the damage to the meat of the nut.
These machines were also advantageously useable for other nuts, as is the subject machine. The machine of the '248 patent, utilized a metered feed mechanism to trap a nut between the counter rotating blades of a shell splitting mechanism. The shell splitting mechanism had blades that would engage the nut shell and split the shell with a shear action. The machine is particularly effective in producing shelled nuts with minimum crushing and damage to the surface of the meat. However, the operation of the machine is most effective when the nuts are of reasonably uniform size, such that the action of the rotating blades has a consistent effect on engaging and splitting the shell. Furthermore, because of the precision in which the nut must be lodged between the splitting blades of the referenced device, devising a mechanism that accurately situates the nut between the rotating blades becomes difficult. Finally, because of the particular construction of a hard-shelled macadamia nut, the shell is often split while leaving the meat attached to the shell. These difficulties have led to the development of newer machines for further optimizing production.
The nut cracking device of U.S. Pat. No. 5,115,733 resolves certain of the problems occasioned by the nut splitting device. The use of two plates mounted on skewed axes allowed nuts of greater dimensional variety in a batch to be cracked. Furthermore, the machine provided an efficient back-up to the shell splitting machine and operated as an efficient re-cracker for nuts that passed the shelling machine uncracked or insufficiently cracked to liberate the meat. However, the compression action by the opposed plates on the nuts tended to damage the meat more than necessary. Also, certain smooth surfaced, hard shelled nuts such as the macadamia, tended to escape the grip of the two plates and pass the process uncracked.
In order to combine the best features of the previously developed machines, applicants have devised an efficient nut shelling machine that is constructed to shell nuts using both a compressive and a shear force. The design of the nut cracking machine permits greater variations in size than does the nut splitting machines described above and is constructed to minimize precision in metering the feeding of nuts to the cracking unit. Finally the invented machine is constructed to inhibit escape of nuts before being shelled. The nut cracking machine is designed to operate on a wide variety of shelled nuts and is particularly adaptable for shelling the round, thick-shelled macadamia nut.